1. Field of the Invention
The present invention relates to an information processor and an information processing method, a display device, and a program, and more particularly to an information processor and an information processing method, a display device, and a program each of which is capable of suppressing deterioration of signal quality after completion of execution of FFT (Fast Fourier Transform) processing in OFDM (Orthogonal Frequency Division Multiplexing) demodulation.
2. Description of the Related Art
An Orthogonal Frequency Division Multiplexing (OFDM) system is proposed as a modulation system for terrestrial digital broadcastings. This system, for example, is disclosed in Japanese Patent Laid-Open No. 2005-303440. The OFDM system means a system in which a large number of orthogonal carriers are used, and each of the orthogonal carrier waves is modulated with either Phase Shift Keying (PSK) or Quadrature Amplitude Modulation (QAM).
With the OFDM system, since the entire transmission band is divided into parts for a large number of sub-carriers, the band per one sub-carrier becomes narrow, and a transmission speed becomes slow. However, the OFDM system has the feature that the OFDM system is no different from the existing modulation system when the perspective of a total transmission speed is considered.
In addition, the OFDM system also has the feature that a symbol speed becomes slow because a large number of sub-carriers are transmitted in parallel with one another. For this reason, it is possible to shorten a time length of a multi-path relative to a time length for one symbol. As a result, the OFDM system also has the feature that the OFDM system is hardly influenced by the multi-path.
Moreover, in the OFDM system, data is allocated to a plurality of sub-carriers, respectively. For this reason, a transmission circuit can be configured by using an Inverse Fast Fourier Transform (IFFT) arithmetically operating circuit for carrying out inverse Fourier transform in a phase of modulation. In addition, a reception circuit can be configured by using a Fast Fourier Transform (FFT) arithmetically operating circuit for carrying out Fourier transform in a phase of demodulation.
With the OFDM system, transmission of a signal is carried out by a measure called an OFDM symbol.
FIG. 1 is a diagram showing the OFDM symbol.
As shown in FIG. 1, one OFDM symbol is composed of an effective symbol as a signal interval for which IFFT processing is executed in a phase of transmission, and a guard interval (hereinafter referred to as “a GI”) for which a waveform of a part of the second half of the effective symbol is copied. The GI is inserted into a position before the effective symbol on a time axis.
A plurality of OFDM symbols as described above are collected, thereby forming one OFDM transmission frame. For example, an Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) standard is set as a standard for the terrestrial digital broadcasting in Japan. In this ISDB-T standard, one OFDM transmission frame is formed from 204 OFDM symbols.
On a reception side for receiving the OFDM transmission frame, the FFT processing is carried out for the effective symbol of each of the OFDM symbols, thereby carrying out the OFDM modulation.
However, under a multi-path environment, in addition to a dominant wave as a direct wave, a delayed wave which arrives after being delayed by a predetermined time relative to the dominant wave exists in some cases. In such cases, even for the same OFDM symbol, an arrival time is different between the OFDM symbol in the dominant wave, and the OFDM symbol in the delayed wave. Then, there is caused an Inter-Symbol Interference (hereinafter referred to as “an ISI”) as an interference between the different OFDM symbols.
When the delayed wave arrives within a time domain not exceeding the GI from the arrival time of the dominant wave, an interval which is not yet affected by the ISI can be utilized as the interval for which the FFT processing is executed. As a result, it is possible to prevent the deterioration of the signal quality after completion of the execution of the FFT processing.